Method of removing gases from inclosed spaces



Patented June 21, 1932 UNITED STATES PATENT OFFICE HENRY MILLER, OFNEWARK, NEW JERSEY, ASSIG-NOR TO NEW PROCESS METALS COR- PORATION, OFNEWARK, NEW JERSEY, A CORPORATION OF NEW JERSEY METHOD OF REMOVING GASESFROM INCLOSED SPACES m Drawing. Application filedAriril 15,

My invention relatesto' improvemeiits in methods of removinggases frominclosed spaces and Whiletheinvention in "its broader aspects maybeapplied to the removal or fixation 0t gasesin various arts, it isparticularly useful in connection with the removal'or ligationof gasesin radio tubes or vacuum bulbsin order'to clean up orget the most ofthere'maining gases therein after the same have been evacuated or mostof the air etc. withdrawn therefrom by "pumping. Certain metalliccompounds or bodies have heretofore been used *in such devices for thepurpose of getting or' combining with or absorbing suoh residualobnoxious gases and for such purposeit has been common to place a smallquantity the metallic body or compound in the 'vacuumtubeor inclosedspace and a-fte'r the tube hus been evacuated,= then heat the body orcompound in-tlie tubeto such an extentth'atitreacts with the residualgases and combines oi absorbs the same to a more or lesse'xtent. I

I have discovered, however, that-if cerium or certaiii ce'rium compoundsor bodies con taining one or more of the cerium group of rareearth'metals are used as getters for this purpose, the residual gasesmay be more efficiently removed and also in many cases theres-ultantvacuum bulb or tube is rendered more eflective thereby.

While'cerium and many "of its alloys with other metals and compounds ofthe metals may be used, I prefer to use an alloy of cerium and certainother metals and preferably one which contains certain nitrides andsulioxides of some of these metalsand I find that when such metallicbodies or compounds are used as getter-s and plaeed in vacuum tubes orbulbs in the usual way and then heated until thy'become active incombining with the ases in the space in the; tube or bulb theresiualjobn'oxious gases therein are more efiicientl'y absorbed andcombined with the getter? material. v

'While' various methods may be used for producing such improved getter?material, I prefer to obtain the same in the following manner. First anelectrolyte is madecontaining cerium and other minerals'of the rare1926. Serial No. 102,307.

earth group. Instead of starting with natural cerium minerals, I preferto use the waste obtained in the manufacture of lanthanum or thorium.This waste occurs as a'yello'wish mud and contains a relatively largequantity of cerium and small quantities of certain other metals of therare earth group such as lanthanum etc. This mud may be obtained as aby-product in the process of making thorium or lanthanum for the gasmantle industry. In any event, I prefer to take the cerium contain ingmaterial and dissolve ism hydrochloric acid and then clarify and'filterthe solution and evaporate the same to dryness, the resultant chloridesof cerium etc. are thus produced in solid form and the same is thenbroken up and gradually added to an electric furnace wherein the metalsare separated fromthe chlorine in the manner described in Hirsch U. S.Patent 1,273,223.. At the endof' the'ruir as described in said patent,the heat andicurr rent are shut off and the material cooled; therein andafter it is cooled, the aiggliomen ated metal alloy called misch-metalis removed. Some of the iron from the furnace will usually have becomealloyed vwith the metal, usually from 2% to 30%, so that the resultingalloy will not only contain a substantial amount of cerium but also from2% to 30% of iron and certain quantities of other rare earth metals andalso some carbon from the carbon electrode of the furnace.

While metallic cerium may be used as etter, I find that such an alloy,obtaine as above, is more advantageous in that the iron which seems torender the'alloy more pyrophoric also seems to make it serve better as agetter for gases in vacuum tubes as above described. I find, however,that even this alloy may be greatly improved as a getter for such gasesby further, refining it or treats ing it and for this purpose Ipreferably place the alloy in a crucible and-melt under a layer. ofbarium chloride as described inHirsch Patent 1,290,010. I believe thatby thus melting the misch-metal alloy under a layer of barium chloridewhich keeps it out of 0011-: tact with the atmosphere, the alloy ispurified in such a way as to remove certain gases and impurities,whereby it is rendered more active for getter purposes. I believe thisis brought about by reason of gases being driven off by the alloy intothe barium chloride. If the melt be, now allowed to cool and the batchof metal alloy separated from the crucible and layer t barium chloride,it will be found to hare much better properties as a getter for gases.

However, I find that it is still possible to inereasefts activity as agetter if instead of allowing the melt to cool i'n-tlie crucible themolten metal is pouredthrough a small hole in the barium chloridelayerinto suitable molds whereby it is cast, in small ieces as describedin said Hirsch Patent 1,2 0,010. I believe he increased a ivity of thema finial-Jim getter; purposes thus produced is dueitmtihei factthat'whfln the alloy is poured into-tho molds itcomes more orjless inconactwith theoaiv whereby nitrogen and oxygflmofi the-air uniitsrwith'some of the rare earth imetalsfionming nitrides thereof and unsaturated;oxides; or suhoxidbs oh the; rare earth metals; particularly of thecerium group at the race s-arch meta-ls.- These niridssiand unsaturatedoxides or suboxides, ltzhslieve, readily dafhsethroughthe .batchmhlmnltea metal; :astit ixs being poured a d.

castaifiovvever; since-thetime that the molten metal namaiusin contactWiiththe air is very sholltt fihfli eilfimblwfifiiant tlme fort-he batchofi metal as! a; whole toihecom-e' thoroughly axfiflimd'bwt thorbadyioflcast alloy so made does contain 1? bclievosubstantiial quantities ofnitriidesand suhoxidesiwhich I" believe greatlyactivatei the: materialficr getter purposes, 1 11:5111)" event I find that when the matsri alhas bee'nso treatediand activated-it shows a: strong a'lfinity fonman'ygiasessuch aswolsvgem or nitrogen and servemespocially well for theremoval ct gases from! vacuum tubes and: the like as above described.

d2s ahouerpoinied out a-ismalli quantity of carbon will be found iutihealloy andthis 13 believe moreon less comllineswith various ostthie rareearth metals to :form carbides and such carbides of the rareeartlimetals and particularly ofthoseofi the ceriumig'mup of rare earthmetals, also seem to improve. the alloy material for gettenpurposesi. I

I also .find that thegetberpropea'ties of the material may'beifuntherimproved by incl ud ing in the mischmetal alloy small quantities of' oneor more metals of the alkali and al kaline earth groups, such aspotassium, sodium, magnesium calcium etc. These metals arepreferablyadded in metallic form to the casting melt; tame, the meltwhich is madeunder the l" r of barium chloride. These nietirls'p'roba lvrmain in thematerial large- I in the metallic form, although it is probable iat tosome extent-they are converted into the: form of carbides, nitridesand/or sub oxides (62 It may also be that some at the; metals: in the,material may: bevin the form of hydrides since in the electrolyticprocess in the electric furnace, I believe some hydrogen is set freewhich would likely bring about such combinations. I prefer to use amaterial in which the alkali and alkaline earth metals taken as a wholedo not constitut'e more than about by weight of the material. Othermetals may be added to the resulting alloy with more or less advantageas a substitute for or in addition toth'e iron, including other metalsof the iron group such as nickel, cobalt, etc, Also the addition of,certain amounts of aluminum and magnesium seemstomake the resultingmaterial particu'- larly efi'ective.

I believe that thertreatment whereby small quantities of the metal ormetals are con" verted to nitrides or suboxides is of particularimportance for activating the material in order that it may be mostelficient for remoring gases from vacuum tubes and the like, In anyevent the treatment above described; does produce a materiali which istar more active for removing gases than the pureoe'= riummetal or thesimple pure alloy of ceriumand other rare earth metals. Theaddition of;iron, nickel, cobalt and other metalsiot the? iron group, Ibelieve, makethe alloy more easily workable and more stable in; theair at ordinarytemperatures, =Such addition also seems to prevent the alloy inoperation from becomingentirely coated with saturatedoxidc or to such anextent that the interior of the body of thematerial is prevented fromacting. effectively as desired,

VVhenapiece of sushi misoh-metal material is secured to the so-calledplate in a radio vacuum bulb and heated for exampleasbv means of asurrounding high frequency; coil, the gases in the tube are given offtherein from the metal parts in the tube as tho-same; are heated andappear to react with the material. If no such iron or equivalent metalis present in the: material, the getter material, seems to be morequickly covered with a layer of oxide or other material whichsubstantially entirely inclosesrthe active material andfthus seems toprevent proper operation of the ma terial as a getter. But with the ironand/or other equivalent metals present, such an in, closing layer seemsto be. prevented and the material acts'more efiiciently for the purposesin question. Furthermore I believe that by varying thezproportion ofiron or other metals or compounds in the material, the melting point andthe point of activation of the getter material may be advantageouslyadjusted, That is, with the ironor otherequivalent metals or materialsincluded in the getter mate-v rial, the getter material seems to act toabsorb or combine with the gases as described, but still rema nas a bodyof. ma e ia n ts-orig and position,

Thusl believethat by including such compounds as nitrides, carbidesand/o1; suboxidcs,

the getter material is made to contain certain relatively unstablecompounds which become active or kindle at a temperature below themelting point of the metal of the material.

The addition of the alkali and alkaline earth metals I believe improvethe material by lowering the melting point of the resulting alloy and solowering the temperature to which the material must be heated before itis sufficiently active to readily combine with or absorb the residualgases in the tube. The presence of these alkali and alkaline earthmetals also seem to regulate the action to some extent which I believeenables the material to more thoroughly combine with the residual gasesfrom all portions of the bulb or space from which the gases are to beremoved. If desired, a small amount of carbon may be added to the meltunder the layer of barium chloride in order that more of the carbidesmay be produced in the resulting alloy material. I have found that analloy of cerium misch-metal and containing also iron, aluminum,magnesium, calcium, potassium and carbon and containing some nitridesand sub oxides of various of these metals is particularly efiicient forthe purposes in question and may be readily prepared in the manner abovedescribed. Such an alloy material is highly pyrophoric; that is, whenscratched or abraded it will evolve showers of sparks, and myinvestigations indicate that such pyrophoric materials serveparticularly well for the removal of gases as described. However, manyof these metals and compounds may be omitted and still a good gettermaterial may be obtained.

While I have described my improvements in great detail and with respectto certain preferred embodiments thereof, I do not desire to be limitedto such details or embodiments since many changes and modifications mabe made and the invention embodied in wi ely different forms withoutdeparting from the spirit and scope thereof in its broader aspects.Hence I desire to cover all equivalents and all modifications and formscoming within the language or scope of any one or more of the appendedclaims.

What I claim as new and desire to secure by Letters Patent is:

1. As an article of manufacture a thermionic tube having a gettermaterial containing an alloy of cerium and other metals hav ing anitride and suboxide of certain rare earth metals therein.

2. As an article of manufacture a thermionic tube having a gettermaterial containing an alloy of cerium and other metals including ametal of the iron group and having a nitride and suboxide of certainrare earth metals therein.

3. As an article of manufacture a thermionic tube having a gettermaterial containing an alloy of cerium, misch-metal and iron,

HENRY MILLER.

